ColorReplace does just that. It replaces a color 
in (.bmp .gif .jpg .png ...... ) images. It changes
one color per pass.
Welcome to QuickerThanASpark.
Below you can find some of my Windows Freeware. 
I have included the sourceCode to showcase HOTBASIC, 
An incredibly quick and powerful programming language.
And below that, you can find some links you may find interesting.
hbSort is a handy little Sort program with lots of sort options. Data can be input/output via a file or copied to/from Clipboard.
hbPalette builds a Palette from any  image. Palettes can be savedToFile or copied to the clipBoard.
hbPalette
hbSort